1. Field of the Invention
The present invention relates to logic circuits and more particularly to logic circuits which provide optical outputs.
2. Description of the Prior Art
It has previously been proposed by H. F. Taylor in an article entitled "Guided Wave Electro-optic Devices for Logic and Computation", Applied Optics 17, 1978, pp 1493-1498, to provide optical logic elements using the electro-optic effect to produce optical outputs in response to electrical inputs.
Further, high speed, high sensitivity photoresponse has been demonstrated in GaAs FETs as reported by C. Baack, G. Elze and G. Walf, in an article entitled "GaAs MESFET: A High-Speed Optical Detector", Electronics Letters 13, 1977 pp. 193-194; J. J. Pan, "GaAs MESFET For High-Speed Optical Detection", Technical Digest of the 22nd SPIE International Technical Symposium, Aug. 28-31, 1978, San Diego, Calif.; J. C. Gammel and J. M. Ballantyne, "The OPFET: "A New High Speed Optical Detector", Technical Digest of the International Electron Devices Meeting, Dec. 4-6, 1978, Washington, D.C.; and J. M. Osterwalder and B. J. Rickett, "GaAs MESFET Demodultes Gigabit Signal Rates from GaAs Injection Laser", Proc. IEEE 67, pp. 966-967, 1979.
The photosensitivity appears to be due to the modulation of channel conductivity by optically injected carriers. It appears that photodetectors operating by this mechanism can have better high frequency performance than photodiodes and for this reason there is considerable interest in developing Gallium Arsenide field effect transistor photodetectors as receivers in high-speed optical communications systems. The properties of FET photodetectors do not, however, exactly parallel those of photodiodes, so that other uses that are not immediately apparent are also appropriate.